Massive Blood Loss Definition in ml/hr
Massive blood loss is defined as blood loss at a rate of 150 mL/min (9,000 mL/hr) or 1.5 mL/kg/min for ≥20 minutes in a 70 kg adult. 1
Primary Rate-Based Definitions
The most clinically relevant rate-based definition from authoritative guidelines specifies:
- 150 mL/min (equivalent to 9,000 mL/hr if sustained) 1
- 1.5 mL/kg/min for ≥20 minutes (equivalent to 105 mL/min or 6,300 mL/hr in a 70 kg patient) 1
These definitions come from the Israeli Multidisciplinary rFVIIa Task Force guidelines and represent the threshold at which conventional hemostatic mechanisms fail and require aggressive intervention. 1
Volume-Based Definitions (Converted to Hourly Rates)
While not strictly ml/hr definitions, the following volume-based criteria can be extrapolated to hourly rates:
- Loss of 50% of blood volume within 3 hours: This translates to approximately 1,167 mL/hr in a 70 kg adult (assuming 7,000 mL total blood volume) 1, 2
- Loss of entire blood volume within 24 hours: This equals approximately 292 mL/hr sustained over 24 hours (10 units of packed RBCs in 70 kg patient) 1, 2
Critical Context for Spinal Cord Injury Patients
In patients with suspected spinal cord injury, hypotension should be attributed to blood loss rather than neurogenic shock until proven otherwise. 3 This is crucial because:
- Only 24% of penetrating spinal cord injury patients were hypotensive in the field, and 74% of those with hypotension had significant blood loss as the cause 3
- The classic presentation of neurogenic shock (hypotension with bradycardia) occurred in only 7% of complete spinal cord injuries 3
- A careful search for bleeding sources is mandatory before attributing hypotension to spinal injury alone 3
ATLS Classification Context
The Advanced Trauma Life Support system defines massive blood loss as >40% of total blood volume (>2,000 mL in a 70 kg adult), which represents Class IV hemorrhagic shock. 2 While this is not an hourly rate, it provides the threshold at which blood loss becomes immediately life-threatening and requires immediate massive transfusion protocol activation. 2
Clinical Application
Activate your massive transfusion protocol immediately when any of these rate-based criteria are met, without waiting for laboratory confirmation. 4 The nature and mechanism of injury (penetrating trauma, major spinal surgery, multiple trauma sites) should alert you to probable massive hemorrhage before formal volume thresholds are reached. 1, 4
For spinal surgery specifically, blood loss >5 liters intraoperatively has been used as a threshold for massive bleeding in research contexts, though this represents cumulative rather than hourly loss. 5